1. Field of the Invention
The present invention relates to transport block size signaling, and more specifically to transport block size signaling based on modulation type.
2. Discussion of the Related Art
In systems that include mobile devices, packets are generally sent using one of many modulations schemes. All packets sent during a given transfer generally conform to the same transport block size (TBS). The sender of the packets sends the receiver information telling the receiver the modulation scheme and transport block size, among other things, before the packets are sent. Therefore, once the packets are sent, the receiver knows the modulation scheme, the number of multicodes, and the transport block size of the packets and, therefore, can correctly decipher and receive the information.
Currently, much discussion has been centered around increasing the number of bits allocated for the definition of the transport block size (currently 6 bits) to allow for a higher resolution. These discussions have been particularly common with those involved in 3GPP (Third Generation Partnership Project) standardization work. Specifically, those individuals working in areas related to Wideband Code Division Multiple Access (WCDMA) and High Speed Downlink Packet Access (HSDPA). In HSDPA, the TBS is placed, along with other information, in the high-speed shared control channel (HS-SCCH). FIG. 1 shows a diagram of current allocation of HS-SCCH signaling bits.
One suggestion is a mapping of the transport block sizes through a logarithmic conversion to minimize the worst-case relative padding in case the MAC-PDU is not of the exactly same size as the available transport block sizes. This is discussed in document R2-0221668, entitled “Signaling of Transport Block Sizes for HS-DSCH” (Ericsson). However, this approach assumes a fixed number of bits for the signaling of the transport block size, and the transport block sizes are dependent on the modulation and multicode setting. Therefore, in cases where a packet is transferred and an error has occurred and retransmission is requested, the retransmission according to this approach, must occur using the same modulation scheme. Thus, a transmitting device (e.g., base station) cannot freely select a modulation scheme whenever a retransmission is required.